1. Field of the Invention
This invention relates to MPEG decoding devices (where xe2x80x9cMPEGxe2x80x9d is an abbreviation for xe2x80x9cMoving Pictures Expert Groupxe2x80x9d) that decode video signals and/or audio signals which are compressed based on the MPEG system, and particularly to MPEG decoding devices that are capable of decoding multiple bit streams.
2. Description of the Related Art
Recently, bit streams that are produced by compression based on the MPEG system are used for video signals (representing moving pictures) and audio signals (representing sound and/or speech) which are subjected to transmission by the satellite digital broadcasting. For this reason, television receivers that receive signals of the satellite digital broadcasting install MPEG decoding devices for decoding the bit streams compressed by the MPEG system.
A conventional example of the MPEG decoding device contains a PES decoder, a code buffer, a time information buffer and an MPEG decoder. Herein, the PES decoder receives prescribed bit streams called xe2x80x9cpacketized elementary streamsxe2x80x9d (namely, PES) to divide them into PES headers and elementary streams. The code buffer temporarily stores the elementary streams that are isolated by the PES decoder. The time information buffer temporarily stores time information contained in the PES headers. Thus, the MPEG decoder decodes the elementary streams, temporarily stored in the code buffer, in connection with the time information that is temporarily stored in the time information buffer.
The conventional MPEG decoding device is designed to decode a single bit stream at once. For this reason, the conventional MPEG decoding device needs a single PES decoder and a single time information buffer. It is rational to employ in the MPEG decoding device for decoding a single bit stream a temporary storage configuration such that the PES decoder is followed by the code buffer for temporarily storing the elementary streams, which are isolated from the packetized elementary streams by removing the PES headers. As compared with a typical code storage for storing original packetized elementary streams accompanied with the PES headers, the aforementioned temporary storage configuration is advantageous in saving a storage area of the code buffer that merely stores the elementary streams being isolated from the original packetized elementary streams by removing the PES headers.
Recent trends in broadcasting provide users of the television receivers with plenty of channels by digital technologies. For this reason, engineers are requested to develop advanced MPEG decoding devices that are capable of coping with plenth of channels in broadcasting. Therefore, the engineers propose extended functions for the MPEG decoding devices, each of which is conventionally designed to decode a single bit stream at once, such that multiple bit streams can be decoded at once.
FIG. 6 shows an example of the MPEG decoding device that is capable of decoding multiple bit streams at once. Concretely speaking, the MPEG decoding device of FIG. 6 is designed to simultaneously decode three bit streams (or three packetized elementary streams). Namely, an MPEG decoding device 100 inputs three packetized elementary streams (PESs) A, B and C. Those streams respectively contain picture data being compressed by the MPEG system.
The PES A is subjected to separation to a PES header and an elementary stream A by a PES decoder 101A. The elementary stream A is temporarily stored in a code buffer 102A. At the same time, time information contained in the PES header is forwarded to a time information buffer 104A via a time information holder 103A, so that the time information is to be temporarily stored in the time information buffer 104A.
The aforementioned configuration corresponding to a set of the PES decoder, time information holder and time information buffer is similarly applied to the other PESs B and C. Namely, the PES B is subjected to separation to a PES header and an elementary stream B by a PES decoder 101B. The elementary stream B is temporarily stored in a code buffer 102B. At the same time, time information contained in the PES header is forwarded to a time information buffer 104B via a time information holder 103B, so that the time information is to be temporarily stored in the time information buffer 104B.
Similarly, the PES C is subjected to separation to a PES header and an elementary stream C by a PES decoder 101C. The elementary stream C is temporarily stored in a code buffer 102C. At the same time, time information contained in the PES header is forwarded to a time information buffer 104C via a time information holder 103C, so that the time information is to be temporarily stored in the time information buffer 104C.
The MPEG decoding device 100 employs a single MPEG decoder 107 that performs decoding on the three streams by a time division system. So, a selector 105 selects one of the three elementary streams A, B and C based on the time division system. In addition, a selector 106 selects the time information suited to the elementary stream presently selected by the selector 105 by the time division system. That is, the selectors 105 and 106 operate in synchronization with each other.
However, the conventional configuration of the MPEG decoding device that is designed to simultaneously decode multiple bit streams bears various problems, which will be described below.
The aforementioned MPEG decoding device should install multiple sets of the PES decoder and time information buffer respectively in connection with multiple packetized elementary streams. This increases a circuit scale of the MPEG decoding device considerably.
In synchronization with inputting of the elementary stream, the MPEG decoder inputs the time information corresponding to each of pictures in the elementary stream. In order to properly match the time information with each picture, the time information is being managed by the FIFO (namely, first-in-first-out) system in the time information buffer. The MPEG decoder performs the aforementioned operations on the multiple streams respectively. This makes management of the time information complicated.
It is an object of the invention to provide an MPEG decoding device that performs simple management on time information with a relatively small scale of circuitry.
An MPEG decoding device of this invention is designed to decode multiple packetized elementary streams (PES) representing video signals and/or audio signals, which are bit streams compressed by the MPEG system in satellite digital broadcasting, for example. Herein, the multiple packetized elementary streams are stored in code buffers respectively. A selector selects one of the packetized elementary streams by a time division system, so that a PES decoder separates the selected packetized elementary stream to a PES header and an elementary stream. A time information holder holds time information being extracted from the PES header. An MPEG decoder decodes the elementary stream with reference to the time information. Namely, the MPEG decoder decodes pictures of the elementary stream in a decode order in connection with the time information, then, decoded pictures are rearranged and output in a display order. Because of provision of a single set of the PES decoder, time information holder and MPEG decoder with respect to processing of multiple packetized elementary streams, it is possible to reduce a circuit configuration of the MPEG decoding device in scale, and it is also possible to provide easy management on relationships between pictures and time information.